TROCHUS. 295 



of Gibbula and the typical section Ziziphinus, which 

 last has a pyramidal spire. It is also not generally 

 known, but not less the fact, that young shells of T. 

 lineatus (the type of Trochocochlea) are always deeply 

 umbilicate. 



A. Small, pearly, and umbiHcate. Margarita , Leach. 

 1. Trochus helici'nus^, Fabricius. 



T. helicinus, Fabr. Fn. Groenl. p. 393 ; F. & H. ii. p. 531, pi. Ixviii. 

 f. 4, 5, Ixxiv. f. 10, and (animal) pi. C C. f. 4. 



Body orangecolour, the upper part marked with close-set 

 longitudinal purple lines or streaks : paUial lappets oval, small, 

 purplish-grey : head short and rounded, semicircular in front, 

 and divided into 12-15 lobes, which form a sort of fringe ; 

 some of these lobes in front are cloven : tentacles slender, 

 flexible and contractile, ringed or annidated, and thickly 

 covered with short ciha giving a bristly appearance; tips 

 blunt : eifes rather large, and there is a supplementary pair of a 

 smaller size on the inner base of the tentacles : foot thick and 

 gibbous, lanceolate, rounded in front and bluntly pointed 

 behind, with a pale line in the middle at the posterior end 

 towards the tail ; sole plain-edged when fully expanded, at 

 other times minutely and irregularly scalloped or jagged at 

 the edges : appendages 6 on each side, annulated and setose 

 like the tentacles ; each filament has a dark eye-like tubercle 

 at its base ; there are sometimes two of these filaments be- 

 tween each of the penultimate and caudal pairs. 



Shell somewhat globular, rather thin, semitransparent and 

 lustrous : scidpture, several slight spiral stria3 on the under 

 side, and occasionally some faint and indistinct spiral lines on 

 the upper side, and a few puckers near the suture ; otherwise 

 the surface is quite smooth and highly polished : colour orange 

 or reddish-brown, sometimes variegated by purplish or azure 

 tints on the upper parts : spire more raised in female than 

 in male individuals ; apex blunt : ivhorls 5, convex and gra- 

 dually enlarging in the former, compressed and rapidly in- 

 creasing in the other sex : suture distinct but not deep : mouth 



* Like a Helix. 



